Above is a map of the WSPR stations that I have received over the past 2 weeks. Because the WSPRnet site map will only display data for up to 24 hours, I used the aprsinfo site to generate this map.
You can see in the map above that the aprsinfo site map code has a “bug” that doesn’t properly map paths that cross the international date line, so my path to VK4YB goes off the left side of the map at the International Date Line and then continues from the International Date Line to VK4YB’s QTH in Moorina, Queensland on the right side of the map. The map engine that I use in my Aircraft Scatter Sharp program had the same bug which I was just alerted to recently by ZL2DX, and it took 12 pages of corrections to fix the problem, which was not in my code, but in the GreatMaps engine .dll file which I had to recode and recompile. So if you are using an old version of Aircraft Scatter Sharp and are planning to do some aircraft scatter or troposcatter across the IDL, as does ZL2DX, then you should download the installer for the latest version of my program from here.
In any event, you can see that my WSPR receive coverage extends over the continental USA and on to Hawaii and to Australia, heading west. I did not copy Europe during the last 2 weeks, even though there were a number of trans-Atlantic WSPR receptions during that period. You can see however from the map of all stations reporting such contacts below, that there were many more WSPR NA–>EU reports (green dots) than EU–>NA reports (red dots), at least over the past 24 hours. I only show the past 24 hours because when one tries to display all WSPR receptions over the past 1-2 weeks, the hard limit placed by the aprsinfo website on the number of reports displayed on the map actually reduces the number of trans-Atlantic reports that get displayed compared with the number displayed for a 24 hour period. The reason for this is obvious if you think for a second or two. It appears that most US stations are not copying Europe consistently, and that only what I would consider to be the “Super Stations” in the USA on 630m are hearing the European spots consistently. I had copied Europe last fall on a few occasions, but have not copied Europe for at least a couple of months. This may be because I had a receive antenna issue that I just discovered and then corrected late on 3-31 UTC…time will tell, but 630m receive conditions will continue to get worse as we move into Spring, so I may have missed my chance for more Eu receptions during this season. Here is the map of WSPR 630m trans-Atlantic receptions by all stations over the past 24 hours:
As I previously noted, my WSPR transmit coverage is NOT as good as my receive coverage; see the map below, which shows my WSPR transmitter coverage, and which is again taken from aprsinfo for the same reason as the maps above.
You can see that my transmitter is well heard over the Eastern half of the USA, to somewhat west of the Mississippi (Dallas, Oklahoma City, and Salem, SD being the 3 Western-most stations copying my 630m WSPR signal).
I would like to extend this coverage at least to the west coast.
My current transmit antenna is an inverted L which was described in previous blogs. It is roughly 15 feet high and 100 feet long. My next iteration transmit antenna will run between trees. I estimate that it will be 60 feet tall and have a 200 foot top hat. If we model this using the 472khz.org calculator to which I have referred many times before in these blogs, and which has worked so well for me, we get the following results for my proposed transmit antenna:
You can see that with ground loss estimated to be 50 ohms, 99.5 Watts Transmitter Power Output is required to put out 5 Watts EIRP, with an antenna current of 1.372 Amps (and an antenna voltage of 2.04kV).
Contrast this with my initial calculation result, shown below, for the 15 ft / 100 foot inverted L I am currently using with same 50 ohm estimated ground loss, where 1492.7W TPO is required to put out 5 Watts EIRP, with an antenna current of 5.158A and an antenna voltage of 17.37 kV!:
I did work on the ground system for my current 15 ft / 100 ft inverted L, as I described in a previous blog, and with that I got the ground loss down to 25 ohms. This did improve my transmit calculations, as you can see in the textbox below, but even so I need 511 W TPO to get 5W EIRP, and my antenna current for 5 W EIRP is 4.054 A and my antenna voltage is 13.65 kV. So the new transmit antenna should be a significant improvement over the old transmit antenna.
And if I reduce the ground loss to 25 ohms for the new transmit antenna, as I did for the old transmit antenna, then the numbers really look good, as you can see in the yellow textbox below: 32.7 Watts TPO to achieve 5W EIRP, with antenna current 1.069A at 5W EIRP, with antenna voltage 1.60 kV.
So I am hoping to reach the West Coast with the new transmit antenna. We shall see. In any event, the above should make quite clear the necessity to optimize the transmit antenna, and particularly the transmit antenna ground, in order to minimize ground losses.
73,
Roger Rehr
W3SZ